That's a really hard-boiled Roman Catholic way to view the world, annalex. I'd thought better of you.
Early Protestant Reformers studied both the Old and New Testaments, and rejected the accumulated layers of corruption, legalism and false doctrine built up over the centuries after Apostolic times, in order to remain true to the purest form of the Gospel. Those traditions and doctrines that withstood this Biblical "test" were retained. The rest were not.
So, this odd hobby-horse you guys have jumped on regarding Sola Scriptura, as if it is some equivalent to the legalism present in your own system of belief, is telling. All traditions, doctrines and teachings are to be tested against the scripture, and those found unscriptural or even questionably so are discarded. That's Sola Scriptura. It was not and is not a repudiation of all tradition and doctrine of the medieval Catholic Church. It was an utter rejection of false doctrine and the traditions of man that had crept into the church that were not Biblically supported.
Regarding the claim that Protestant beliefs were "only possible because people trusted Luther's knowledge of the scripture," well, there's that hardwired expectation of some worldy authority, some mere man, standing in the role of Bishop of Rome, that your ability to process the world apparently seems to depend upon entirely. You've said in the past that you've attended services in a Protestant Church, but this sort of cloistered, provincial ignorance does not support such a claim.
Luther arose more or less contemporaneously with numerous figures in the Reformation. He was no more of a Protestant "pope" with believers in him than the man in the moon. When you find yourself able to grasp this, then you can plausibly claim to know very well "the Protestant doctrines." Until then, you can't.
The scripture indeed praises the scripture, sets it up as a method of resolving disputes and notes that it is divinely inspired. But it never sets it up as a sole rule of faith; it does however set up the Church as the rule of faith.
So, “sola Scriptura” is unscriptural.
I only picked on Luther because he started the deception. Others followed.